1. Field of the Invention
The present invention relates to a rotary dryer used for drying material by passing a mixture of an inlet gas and the material from an inlet and along a material flow path through the dryer and to an outlet. More particularly, the rotary drum dryer hereof has an improved structure which prevents the clogging of the material flow path during operation.
2. Description of the Prior Art
Presently, material, such as wheat straw, long strand alfalfa, wood seltzer, and other elongated strands of material, are dried by being mixed with gas and injected into a rotary dryer having an inlet and an outlet. Once the material reaches the outlet, it is sufficiently dry for use.
It is known in the prior art to provide a rotary dryer for drying material which includes a tubular housing presenting first and second ends, and having first and second tubes mounted in a concentric relationship within the housing. A mixture of inlet gas and material is introduced into the housing, and flows through a material flow path defined by the path extending from the housing into and through the first tube, into and through the second tube, and to an outlet.
The first tube of the prior art presents a first end, and an open second end. A first end plate is mounted to the first tube adjacent to the first tube first end. A second end plate is mounted to the housing adjacent to the housing second end. The first end of the first tube is supported by pedestals extending radially from the housing to the first tube first end. The second end of the first tube is also supported by pedestals which extend radially from the housing to the first tube second end. The open second end of the first tube is in open communication with the housing.
The second tube presents open first and second ends, and is positioned within the first tube. The second tube first end is supported by pedestals extending radially from the first tube first end to the second tube first end. The open first end of the second tube is in open communication with the first tube. The second tube second end is coupled with the second end plate adjacent the second end plate opening.
During operation of the prior art device, the material flows along the flow path through the housing and tubes, and is ejected through the outlet. When introduced, the material is moist and relatively supple. As a result, the material is susceptible to becoming wrapped around structures along the material flow path, thus clogging, or otherwise restricting, the material flow path.
A portion of the material strikes the internal structures, such as the pedestals, and wraps around the pedestals and the other structures. This problem is especially noticed at the points where the material exits the housing and enters the first tube, and where the material exits the first tube and enters the second tube. At these points, the material is required to make a 180.degree. turn, which causes the material velocity to decrease, a factor which further aids in the material becoming wrapped around the structures.
As the portion of wrapped material grows, the flow path becomes increasingly restricted. As a result, the dryer operates at a reduced efficiency, and must be eventually opened and cleaned. Therefore, a significant, and heretofore unsolved, need exists to provide a rotary drum dryer having improved structure which prevents the material flow path from becoming clogged, or otherwise restricted, during operation.